JP2690133B2 - Vending machine induction heating device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating apparatus of a vending machine for heating and selling (hereinafter, referred to as HOT sale) a canned beverage product such as coffee by induction heating. .

2. Description of the Related Art In recent years, there has been proposed a vending machine that applies an induction heating technique and instantly heats a canned beverage product at the time of sale to sell HOT. Most of the heating control methods of the induction heating device of these vending machines are constant time control methods using a timer or the like because it is difficult to directly detect the temperature of the canned beverage product during induction heating.

FIG. 6 shows a configuration diagram of a conventional induction heating device of a vending machine. 1 is a heating coil for inductively heating a canned beverage product 2 stored at refrigeration or room temperature, 3 is a resonance capacitor connected in parallel to the heating coil 1, and 4 is connected in series to the heating coil 1 and the resonance capacitor 3. The power switching semiconductors 5 are diodes connected in antiparallel to the power switching semiconductors 4 for reverse conduction, and these constitute a voltage-type resonant inverter circuit 6. Reactor 7
And the capacitor 8 constitutes a filter. The voltage-type resonance inverter circuit 6 receives a commercial power supply 10 that has been full-wave rectified by the rectifier bridge diode 9 as input, converts the commercial power supply into high-frequency power, and supplies high-frequency power to the heating coil 1 to thereby supply the heating coil. The canned beverage product 2 in 1 is induction-heated. An input current detection circuit 11 detects an input current flowing through the voltage-type resonance inverter circuit 6 and is connected to the inverting input terminal of the differential amplifier 12. The non-inverting input terminal of the differential amplifier 12 is connected to a reference voltage circuit 15 which is composed of resistors 13 and 14 and supplies a constant voltage. Differential amplifier 12
Is configured such that when the voltages at the inverting input terminal and the non-inverting input terminal are equal, the output is 0 volt, and the output terminal is connected to the variable pulse width oscillator 16. The variable pulse width oscillator 16 controls the conduction angle of the power switching semiconductor 4 so that the output signal from the differential amplifier 12 becomes 0 volt. That is, the pulse width for switching the power switching semiconductor 4 is variably controlled. This constitutes a so-called current limiter circuit which regulates the input current to the voltage-type resonance inverter circuit 6 with the voltage set by the reference voltage circuit 15. The output of the variable pulse width oscillator 16 is connected to a drive circuit 17 for switching the power switching semiconductor 4. The differential amplifier 12, the variable pulse width oscillator 16, and the drive circuit 17 form an oscillation control circuit 18. Reference numeral 19 denotes a control circuit of a vending machine (not shown), which receives a sales signal from a product sales switch 20 and operates the oscillation control circuit 18 for a predetermined time.

The operation of the induction heating device of the vending machine configured as described above will be described. First, when the product sale switch 20 is pressed and a sale signal is input to the control circuit 19, the control circuit 19 sends a control signal to the oscillation control circuit 18 for a predetermined time to inductively heat the canned beverage product 2 for a predetermined time. Output. The oscillation control circuit 18 receives the control signal, starts the variable pulse width oscillator 16, and switches the power switching semiconductor 4 via the drive circuit 17. Thereby, the voltage-type resonance inverter circuit 6 is activated, and the induction heating of the canned beverage product 2 is started. When the induction heating is started, a current flows through the voltage-type resonance inverter circuit 6, and the input current detection circuit 11 outputs a voltage signal proportional to the input current. The differential amplifier 12 outputs a difference between the voltage signal and a reference voltage set by the reference voltage circuit 15. And a variable pulse width oscillator
Numeral 16 varies the pulse width (conduction angle) so that the output signal from the differential amplifier 12 becomes 0 volt. That is, the pulse width (conduction angle) is varied so that the output signal from the input current detection circuit 11 becomes equal to the reference voltage value set by the reference voltage circuit 15. It is controlled to be a constant value. Thus, the beverage product 2 in a can is induction-heated with the heating output specified by the input current for the time set by the control circuit 19, and is sold by HOT.

However, in the above configuration, when the input voltage of the voltage-type resonant inverter circuit 6 fluctuates, the final temperature of the canned beverage product 2 after the induction heating fluctuates. FIG. 7 shows the characteristics of the heating output when the input current of the voltage-type resonance inverter circuit 6 is constant and the input voltage is varied by 200 V ± 15% (operating voltage range of the vending machine). In the figure, a shows the characteristics of the input current and b shows the characteristics of the heating output. Electric power (heating output)
Is obtained by multiplying the power factor (efficiency) by the product of the input current and the input voltage. If the input current is kept constant, the heating output as shown in FIG. 7 naturally has a characteristic proportional to the input voltage. In a conventional induction heating device of a vending machine, for example, as shown in FIG. 7, the input current is set to about 12 A so that a heating output of 2.0 kW can be obtained at a rated voltage of 200 V.
When the voltage of the reference voltage circuit 15 is set to be 2 A, when the input voltage fluctuates ± 15%, the heating output fluctuates by about 1.7 KW to 2.3 KW, and the heating efficiency is almost constant.
Will fluctuate ± 15%. For example, 30 ° C
The canned drink product 2 stored in
If it is raised and sold at 60 ℃ (HOT sales temperature), then a variation of ± 4.5 ℃ will occur. In fact, 30
The storage temperature of ℃ also has a variation of about ± 3.0 ℃, the variation of the whole vending machine is ± 7.5 ℃, there was a problem that canned beverage products 2 can not be sold at a stable temperature.

In view of the above problems, the present invention provides an induction heating device for a vending machine that keeps a heating output constant without being affected by an input voltage and sells canned beverage products at a stable temperature.

Means for Solving the Problems In order to solve the above problems, an induction heating device of a vending machine of the present invention comprises a heating coil for induction heating a canned beverage product, the heating coil, a resonance capacitor, and a power switching semiconductor. A voltage-type resonant inverter circuit,
An input current detection circuit for detecting an input current of the voltage type resonant inverter circuit, an input voltage detection circuit for detecting an input voltage of the voltage type resonant inverter circuit, and the voltage type resonant inverter circuit when a heating output is constant. Of at least two correction circuits that approximate the input current characteristic of the input voltage detection circuit and convert the voltage detected by the input voltage detection circuit with different characteristics, and a selection circuit that selects one of the correction circuits; and the input current detection circuit, An oscillation control circuit that receives the output signal from the selection circuit and controls the oscillation of the voltage-type resonant inverter circuit; and a control circuit that receives the sales signal from the product sales switch and operates the oscillation control circuit for a certain period of time. Be prepared.

According to the present invention, with the above-described configuration, the input voltage characteristic of the voltage-type resonant inverter circuit detected by the input voltage detection circuit is corrected by a plurality of correction circuits, and the corrected characteristic is selected by the selection circuit, and the combined voltage type is selected. By approximating the input current characteristics when the heating output of the resonant inverter circuit becomes constant and controlling the input current with the oscillation control circuit using the approximated characteristics, the heating output becomes constant and is not affected by the input voltage. It is possible to heat canned beverage products for a certain period of time with a constant heating output.

Embodiment FIG. 1 is a configuration diagram showing one embodiment of the present invention. still,
Detailed description of the same parts as those in the conventional example will be omitted. Reference numeral 21 is an input voltage detection circuit for detecting the input voltage of the voltage type resonant inverter circuit 6, and its output is the first correction circuit 22.
a, the second correction circuit 22b, and the N-th correction circuit 22n. The outputs of these N correction circuits are input to the selection circuit 23. The selection circuit 23 is configured to select one of the outputs of these correction circuits and input it to the oscillation control circuit 18.

Next, a method for keeping the heating output constant will be described with reference to FIGS. FIG. 2 shows the change in the input current with respect to the change in the input voltage when the heating output is kept constant at 2.0 KW in the voltage type resonant inverter circuit 6. As shown in the figure, if the heating output is constant, the input power is inversely proportional to the input voltage (the power factor is considered to be approximately constant), so if the input current is controlled so as to have the characteristics shown in FIG. It should be noted that the heating output becomes constant. FIG. 3 is a diagram showing a method for approximating the characteristics of this input current. Input current characteristics
A constant heating output can be obtained accurately by approximating with a straight line a for 200 V or more and with a straight line b for 200 V or less. Obviously, if this approximate straight line is refined, a constant heating output can be obtained with higher accuracy.

FIG. 4 shows an example of a specific circuit of a main part. The current detection circuit 11 includes a current transformer 24 for extracting the current flowing through the voltage-type resonant inverter circuit 6 as a voltage value, a load resistor 25 connected in parallel with the current transformer 24 for determining the output voltage of the current transformer 24, and an output voltage It is composed of a rectifying bridge diode 26 composed of four diodes for keeping the peak value, a resistor 27, and a capacitor 28. The input voltage detection circuit 21 is a voltage type resonant inverter circuit 6
The resistors 29 and 30 that divide the input voltage of the input voltage into a low voltage, the divided voltage is input to the base of the transistor 31, and the transistor 31 and the resistors 32 and 33 that hold the peak value of the input voltage It is composed of an emitter follower type peak hold circuit 35 composed of a capacitor 34. The output of the peak hold circuit 35 is connected to the first correction circuit 22a and the second correction circuit 22b. The first correction circuit 22a receives the output from the peak hold circuit 35 and is a voltage follower circuit 36.
And an inverting differential amplifier circuit 37 for correcting the output of the voltage follower circuit 36. The voltage follower circuit 36 makes the input of the first correction circuit 22a high impedance. The inverting differential amplifier circuit 37 includes an operational amplifier 38, resistors 39 and 40 that approximate the slope of the output voltage characteristic of the voltage follower circuit 36 to the straight line a shown in FIG. 3, and a reference input to the non-inverting input terminal of the operational amplifier 38. Resistors 41, 42 that determine the voltage
Consists of The second correction circuit 22b has the same configuration and is composed of a voltage follower circuit 43 that receives the output from the peak hold circuit 35 and an inverting differential amplifier circuit 44 that corrects the output of the voltage follower circuit 43. Voltage follower circuit
43 is for making the input of the second correction circuit 22b high impedance. The inverting differential amplifier circuit 44 includes an operational amplifier 45,
The slope of the output voltage characteristic of the voltage follower circuit 44 is set to the third
Resistors 46 and 47 that approximate the straight line b shown in the figure and the operational amplifier 4
Resistor 4 that determines the reference voltage input to the non-inverting input terminal of 5
Consists of 1,42. The reference voltage is common to the two correction circuits 22a and 22b. The selection circuit 23 is composed of two diodes 48 and 49 connected to the common cathode and a resistor 50 for pulling down the cathode, and the outputs of the inverting differential amplifier circuits 37 and 44 are connected to the anodes of the diodes 48 and 49, respectively. ing. The cathode is connected to the non-inverting input terminal of the differential amplifier 12 in the oscillation control circuit 18. With this configuration, the selection circuit 23 selects and outputs the higher one of the output voltages of the two inverting differential amplifier circuits 37 and 44. Control circuit 19
Is composed of a microcomputer 51 and peripheral circuits. The microcomputer 51 shown here is a CPU, ROM, RA
It is a so-called one-chip microcomputer having an M and an input / output unit. The product sale switch 20 is input to the microcomputer 51 so as to determine whether or not the product sale switch 20 has been pressed. Also,
The microcomputer 51 receives a sales signal from the product sales switch 20, and an output for oscillating the pulse width variable oscillator 16 for a certain period of time is connected to the pulse width variable oscillator 16 in the oscillation control circuit 18.

The operation of the induction heating device of the vending machine configured as described above will be described.

When one of the product selection switches 20 is pressed and a sales signal is input to the microcomputer 51, the microcomputer 51 should inductively heat the canned beverage product 2 for a predetermined time described in the internal ROM. Oscillation control circuit 18
To output a control signal. The oscillation control circuit 18 receives the control signal, starts the variable pulse width oscillator 16, and switches the power switching semiconductor 4 via the drive circuit 17. Thereby, the voltage-type resonance inverter circuit 6 is activated, and the induction heating of the canned beverage product 2 is started. When the induction heating is started, a current flows through the voltage-type resonance inverter circuit 6, and a voltage signal proportional to the input current is output from the input current detection circuit 11 which is composed of the current transformer 24 and holds the peak value of the input current. You. On the other hand, the input voltage detection circuit 21 composed of the emitter-follower type peak hold circuit 35 outputs the voltage characteristic shown in FIG. 5 which is proportional to the change of the input voltage of the voltage type resonance inverter circuit 6. In the first correction circuit 22a, the first correction circuit 22a corrects the reverse characteristics shown in FIG. 3a by the resistors 39 and 40 in the inverting differential amplifier circuit 37. Similarly,
The second correction circuit 22b is an inverting differential amplifier circuit 44 and resistors 46 and 47.
Then, the reverse characteristic shown in FIG. 3b is corrected. That is, the straight line a and the straight line b having two different inclinations are corrected. In addition, the resistor 41, which is connected to the non-inverting input terminal of the operational amplifier 38, 39,
The reference voltage given by 42 determines the intersection of the corrected straight line a and straight line b. In this embodiment, the input voltage
It is set to 200V. Since the selection circuit 23 selects and outputs the voltage having the higher output voltage of the two inverting differential amplifier circuits 37 and 44, the output voltage characteristic of the selection circuit 23 is a straight line a for 200 V or more.
Then, the characteristic of the straight line b is obtained at 200V or less. By this, the input current when the heating output is constant (2.0 KW) is approximated. This output is the differential amplifier in the oscillation control circuit 18.
Input to 12 non-inverting input terminals. Variable pulse width oscillator
Numeral 16 varies the pulse width (conduction angle) so that the output signal from the differential amplifier 12 becomes 0 volt. That is, since the pulse width (conduction angle) is changed so that the output signal from the input current detection circuit 11 becomes equal to the output voltage of the selection circuit 23, the input current of the voltage type resonant inverter circuit 6 changes the heating output. The current characteristics are similar to the input current when it is constant (2.0KW), and the heating output (2.0KW) is almost constant with respect to the fluctuation of the input voltage. As a result, the canned beverage product 2 is induction-heated at a constant heating output for a fixed period of time set by the microcomputer 51, and is sold by HOT.

In this embodiment, the input current is approximated by using two straight lines when the heating output is constant at 2.0 KW. In this case, the accuracy of 2 KW ± 1% (± 0.02 KW) with respect to the input voltage of 200 V ± 15%. The obtained temperature variation was ± 0.3 ° C and the temperature rise characteristics were almost constant.

According to the configuration of the above embodiment, the heating output is constant even when the input voltage fluctuates, so the temperature of the canned beverage product 2 after heating for a certain period of time is constant, and the canned beverage product is always at a stable temperature. 2 can be sold.

EFFECTS OF THE INVENTION As is apparent from the embodiments described above, the induction heating device of the vending machine of the present invention includes a heating coil for inductively heating a beverage product in a can, a resonance capacitor, and a voltage-type resonance inverter circuit including a power switching semiconductor. The input voltage is detected by the input voltage detection circuit, the input voltage characteristics of the voltage type resonant inverter circuit are corrected by a plurality of correction circuits, the corrected characteristics are selected by the selection circuit, and the voltage type resonant inverter circuit is combined. The input current characteristic when the heating output of is constant is approximated, and the heating output is controlled to be constant by controlling the input current with the oscillation control circuit using the approximated characteristic.
Since the control circuit is configured to operate the oscillation control circuit for a certain period of time, it is possible to heat the canned beverage product for a certain period of time with a constant heating output without being affected by the input voltage, and it is always stable. It is possible to sell canned beverage products at temperature.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an induction heating device for a vending machine showing an embodiment of the present invention, FIG. 2 is an input current characteristic diagram of a voltage type resonant inverter circuit when a heating output is constant, and FIG. Second
The figure which approximated the input current characteristic shown in the figure by two straight lines, 4th
FIG. 7 is a circuit diagram of a main part of this embodiment, FIG. 5 is a detection voltage characteristic diagram of an input voltage detection circuit of this embodiment, and FIG. 6 is a configuration diagram of a conventional induction heating device for a vending machine. The figure is a heating output characteristic diagram of the voltage-type resonant inverter circuit when the input current is constant. 1 ... heating coil, 2 ... beverage product in can, 3 ... resonance capacitor, 4 ... power switching semiconductor, 6 ...
Voltage-type resonant inverter circuit, 11 ... input current detection circuit,
18 ... Oscillation control circuit, 19 ... Control circuit, 20 ... Sales switch, 21 ... Input voltage detection circuit, 22a ... First correction circuit, 22b ... Second correction circuit, 22n ... Nth Correction circuit,
23 ... Selection circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-160591 (JP, A) JP-A-52-16651 (JP, A) Actually opened 63-99983 (JP, U)

Claims (1)

(57) [Claims] 1. A heating coil for inductively heating a canned beverage product, a voltage-type resonance inverter circuit comprising the heating coil, a resonance capacitor, and a power switching semiconductor;
An input current detection circuit for detecting an input current of the voltage type resonant inverter circuit, an input voltage detection circuit for detecting an input voltage of the voltage type resonant inverter circuit, and the voltage type resonant inverter circuit when a heating output is constant. Of at least two correction circuits that approximate the input current characteristic of the input voltage detection circuit and convert the voltage detected by the input voltage detection circuit with different characteristics, and a selection circuit that selects one of the correction circuits; and the input current detection circuit, An oscillation control circuit that receives the output signal from the selection circuit and controls the oscillation of the voltage-type resonant inverter circuit; and a control circuit that receives the sales signal from the product sales switch and operates the oscillation control circuit for a certain period of time. An induction heating device for a vending machine, which is characterized by being provided.